Congrats on the new lens! You are right that the lens is very sharp even wide open, and throughout its zoom range, too. It makes an excellent (though not light) walk-around lens, one that's fun to use.

But I went for the 50-135 first as I wanted the SDM, f2.8 and weather sealing for sports.

I can cover most of the shorter focal lengths with a collection of primes for landscape and still life work. I am still lacking a good lens to cover below 28mm.

Love my DA*16-50 as well since it does great indoors for low light wide angle photography. I've read of reports of bad versions of this lens, but mine which I purchased in June 2008 has been great. Only complaint is for a walk about lens, it is a tad bulky (77 mm filter size). I carry both the 16-50 and 50-135 in my backpack together with the Pentax 10-17 Fish Eye. I'd like to get a longer reach DA* lens which leaves me with the DA*300, the yet to be released DA*60-250 which are both f/4's. The alternative is to get the Sigma 70-200 f/2.8.

Love the SDM on the 16-50 (quiet and fast). Must admit that even though it is weather sealed, I've not tested that attribute.